C#：foreach与yield语句的介绍

 foreach (Person p in persons)
 {
 Console.WriteLine(p);
 }

 IEnumerator enumerator = persons. GetEnumerator();
 while (enumerator.MoveNext())
 {
 Person p = (Person) enumerator.Current;
 Console.WriteLine(p);
 }

 yield return <expression>;
 yield break;
 

try
             {
                 // ERROR: Cannot yield a value in the boday of a try block with a catch clause
                 yield return "test";
             }
             catch
             { }

             try
             {
                 //
                 yield return "test again";
             }
             finally
             { }

             try
             { }
             finally
             {
                 // ERROR: Cannot yield in the body of a finally clause
                 yield return "";
             }

using System;
 using System.Collections.Generic;

 namespace ConsoleApplication6
 {
     class Program
     {
         static void Main(string[] args)
         {
             HelloCollection helloCollection = new HelloCollection();
             foreach (string s in helloCollection)
             {
                 Console.WriteLine(s);
                 Console.ReadLine();
             }
         }
     }

     public class HelloCollection
     {

         public IEnumerator<String> GetEnumerator()
         {
             // yield return语句返回集合的一个元素，并移动到下一个元素上；yield break可以停止迭代
             yield return "Hello";
             yield return "World";
         }
     }
 }

using System;
 using System.Collections.Generic;

 namespace ConsoleApplication8
 {
     class Program
     {
         static void Main(string[] args)
         {
             MusicTitles titles = new MusicTitles();
             foreach (string title in titles)
             {
                 Console.WriteLine(title);
             }
             Console.WriteLine();

             foreach (string title in titles.Reverse())
             {
                 Console.WriteLine(title);
             }
             Console.WriteLine();

             foreach (string title in titles.Subset(2, 2))
             {
                 Console.WriteLine(title);
                 Console.ReadLine();
             }
         }
     }

     public class MusicTitles
     {
         string[] names = { "a", "b", "c", "d" };
         public IEnumerator<string> GetEnumerator()
         {
             for (int i = 0; i < 4; i++)
             {
                 yield return names[i];
             }
         }

         public IEnumerable<string> Reverse()
         {
             for (int i = 3; i >= 0; i--)
             {
                 yield return names[i];
             }
         }

         public IEnumerable<string> Subset(int index, int length)
         {
             for (int i = index; i < index + length; i++)
             {
                 yield return names[i];
             }
         }
     }
 }